Roofing shingles are used to provide an exterior covering for a roof which is both weather resistant and attractive in appearance. Asphalt composition shingles are a very popular roof covering because of their relatively low cost, ease of installation, and long life. In addition, asphalt composition shingles can be produced in a large variety of colors or color patterns so that the roof of one residential home does not look the same as the neighboring structure.
Despite the many benefits of using asphalt composition shingles, many homeowners desire a roof having the heavily textured appearance of a roof covered with wooden shakes, tiles, or slate shingles. In pursuit of this desirable textured appearance, many asphalt composition shingles have been devised with a tabbed configuration resembling wood shakes. To further enhance the textured appearance, some tabbed shingles are formed from multiple layers of material laminated into a single shingle. Many such shingles are known having two layers of composition material with at least one of the layers being tabbed. Further, for example, U.S. Pat. No. 4,729,814 (and related U.S. Pat. Nos. 4,775,440 and 4,869,942) discloses a laminated roofing shingle comprising three layers and having exposed tab cutouts two layers thick. Similarly, U.S. Pat. No. 5,195,290 discloses a laminated roofing shingle comprising three layers including tabs and cutouts formed in the upper two layers.
An important factor in achieving a desirable appearance in a roof formed of tabbed asphalt composition shingles is the degree of random variations between the tab configurations of the various shingles. Shingles which have little variations in tab configuration with respect to other shingles on the roof are often perceived as having a bland or cheap appearance, while shingles with many variations in tab configuration will more closely resemble the random texture provided by a shake roof. In addition, the use of shingles with little tab variation or with predictable variation can produce undesirable visual patterns on the roof, for example perceived diagonal lines on the roof known as the zipper effect. It is therefore desirable to produce tabbed asphalt composition shingles having the greatest possible variation in tab configuration.
Conventional two-layer laminated roofing shingles are typically produced by cutting a sheet of asphalt composition material into sets of longitudinal strips, some of which are straight-edged and some of which are tab-edged, at a first station including a combination slitter and tab cutter. The slitter and tab cutter generally comprises a single revolving cutter drum fitted with continuous (i.e., wrap-around) knife edges shaped in the desired pattern to be cut. For example, a slitter is typically a plain (disc-shaped) knife mounted on the drum and used to cut straight-edged strips while a tab cutter is typically a serpentine or zig-zag shaped knife mounted on the same drum and used to cut a line of interdigitating tabs between a pair of tab-edged strips. A single cutter drum usually mounts several sets of knives such that it can make several sets of adjacent straight-edged and tab-edged strips at a single station. After the slitting and tab cutting operation, two-layer laminated strips are formed by overlaying and laminating together one straight-edged longitudinal strip and one tab-edged longitudinal strip at a series of shifting, aligning, and laminating stations. The two-layer laminated longitudinal strips are then cut into uniform lengths in a transverse cutting station to form individual two-layer shingles.
To introduce some variation into the tab configuration, the tab-cutting knife can be patterned to cut a sequence of tabs having slightly different dimensions and/or shapes. However, since the knife pattern on the cutting drum repeats with each revolution of the drum, the cutting drum will always produce the same pattern or sequence of tabs over and over. If the circumference of the cutter drum is the same as the length of the finished shingle, then the same tab pattern will repeat at the same position on every shingle, resulting in a uniform appearance among the shingles. However, to further increase the variation in tab configuration among shingles, it is known to utilize a cutter drum which has a circumference that is different from the length of the finished shingle such that many shingles can be cut before the tab pattern from an earlier shingle is precisely repeated at the same position on a subsequent shingle.
In the three-layer shingles produced by the known method of U.S. Pat. No. 4,729,814, the tab cutter cuts through a two-layer sheet of shingle material to form two-layer tab-edged longitudinal strips. Since the blade of the tab cutter extends radially outward from the surface of the rotating cutting drum, the knife will initially contact the sheet of shingle material at a point some distance ahead of the point of tangency between the surface of the drum and the sheet. This distance results in the knife blade entering the sheet material while moving at an angle to the surface rather than perpendicular to the surface. Due to this inclination, those portions of the blade that are oriented parallel to the axis of rotation of the drum (such as those found on a tab-cutting blade) will tend to crush or gouge the sheet while cutting through. While the extent of such gouging is minimized when cutting a single-layered sheet, the gouging is much more pronounced (and therefore undesired) when sheets having two or more layers are cut. A need therefore exists, for a method and apparatus for making three layer shingles in which the tabs are cut from single-layer sheets of shingle material.
As previously discussed, it is desirable to produce laminated shingles having multiple layers of tabs with a very random tab configuration. Ideally, no two shingles on a roof would have an identical tab configuration. However, when all tabs are cut using tab cutter blades mounted on a single cutting drum, such as in conventional two-layer shingle manufacture and in the three-layer shingles produced by the known method of U.S. Pat. No. 4,729,814, the tabs will have a period of repetition (i.e., the number of shingles that are produced from a strip before another shingle having the same tabs in the same positions is produced) which is based on the relationship between the circumference of the cutter drum and the length of the finished shingle. This relationship limits the variations in tab configuration among the shingles. A need therefore exists, for a method and apparatus for producing laminated roofing shingles having a greater number of variations of tab configurations than existing laminated roofing shingles.